Issue #17415: Clarify 'this' referent by moving containing sentence just after
the sentence referred to. Make other minor edits to improve flow.
Merge with 3.2
Issue #17415: Trim trailing whitespace
Merge with 3.2
Issue #16880: _imp.load_dynamic() is not defined on a platform that
does not support dynamic loading (e.g. Atari), so make sure that imp
doesn't assume it always exists.

Patch by Christian Heimes.
#16057: Clarify why the base method default is called in custom encoders.

Original patch by Kushal Das.
Merge #16057: Clarify why the base method default is called in custom encoders.

Original patch by Kushal Das.
#17448: Make test_sax skip if there are no xml parsers.

Patch by Rafael Santos.
Merge #17448: Make test_sax skip if there are no xml parsers.

Patch by Rafael Santos.